How many Istari came to Middle-earth?

[Finwe]

You've got a good point there. I think that was another one of the little mysteries that the good ol' Professor threw in there to make all his readers nearly pull their hair out in frustration. It's like that line, when Eowyn killed the Witch-king,

...was not heard in this Age of the World.

I'm sure he enjoyed putting in little mysteries like that just to make us think. I personally believe that there were five Istari worth mentioning, that is why only their names are given. If there were any others, then they either failed almost immediately, or got themselves killed. Either way, they weren't of any consequence, and that was why they weren't mentioned.